One possibility is to get a smartphone screen protector and just cut it down to size.
I do this for all my gear with displays.
Ebay is fine, or even spamazon, look for older phone model covers like iPhone 3 4 or 5 - whoever has those things wants to get rid of them for next-to-nothing, I am sure. Free Shipping on a sub-99-cent item makes this a slam-dunk.
I don't have a best method for it, but I think I always cut it to shape with all the backing on, so it's not sticky, and get it as close as I can before peeling it. Remember, you can always trim more, but if you over-cut, you'll need to start over. One phone protector should cover a couple M10 screens though, so you can try again even if you don't buy a three-pack!
The covers come with a cleaning cloth, and instructions on how to apply, try to do it smoothly so you don't get bubbles in there.
Edit: I just remembered, I have two iPhone3 skins side-by-side covering my magic trackpad because it was making my fingertips cold on cold mornings!!!!!